Amides infrared absorption

Scheme 30) (6). Infrared spectra of the products possess a normal amide carbonyl absorption, indicating that the products are not present on the dipolar form (30) but rather as the neutral A -thiazoline tautomer (31 or 32) (6). 

The UV-spectra of azolides have already been discussed in the context of hydrolysis kinetics in Chapter 1. Specific infrared absorptions of azolides were mentioned there as well increased reactivity of azolides in nucleophilic reactions involving the carbonyl group is paralleled by a marked shift in the infrared absorption of the corresponding carbonyl bond toward shorter wavelength. For example, for the highly reactive N-acetyl-tetrazole this absorption is found in a frequency range (1780 cm-1) that is very unusual for amides obviously the effect is due to electron attraction by the heterocyclic sys-tem.[40] As mentioned previously in the context of hydrolysis kinetics of both imidazo-... 

Formation of an amide is also indicated in the reaction of PCTFE with Cr(CO)6 and the primary amine, benzylamine. The infrared absorption spectrum shows an N-H stretch centered at 3400 cm, aromatic C-H stretches at 3063 and 3030 cm1, aliphatic C-H stretches at 2933 and 2876 cm1, a broad amide I/amide II band ranging from 1680-1580 cm1, and a C-N stretch at 1454 cm1. The C-Cl stretch at 970 cm1 also shows a significant decrease in... 

Morrissey 53) used transmission infrared spectroscopy to study protein adsorption onto silica particles in a heavy water (DzO) buffer. By observing the shift in the amide I absorption band, he could deduce the fraction of protein carbonyl groups involved in bonding to the silica surface. He found that bovine IgG had a bound fraction of 0.20 at low bulk solution concentrations, but only about 0.02 at high solution concentrations. However, neither prothrombin nor bovine serum albumin exhibited a change in bound fraction with concentration. Parallel experiments with flat silica plates using ellipsometry showed that the IgG-adsorbed layers had an optical thickness of 140 A and a surface concentration of 1.7 mg/m2 at low bulk solution concentration — in concentrated solutions the surface amount was 3.4 mg/m2 with a thickness of 320 A (Fig. 17). 

Here A refers to cryosublimation, B to infrared absorption, and C to gel filtration. 1 Data of Leach and Hill (290). c Amide + amino only. d Peptide NH only. 

A similar translation scheme from the full quantum approach to a mixed quantum classical description has been used recently in Ref. [26-29] to calculate infrared absorption spectra of polypeptides within the amide I band (note that the translation scheme has been also used in the mentioned references to compute nonlinear response functions). 

There is the 3 methods for preparing of 8-azaspiro(4.5)decane-7,9-dione, 8-(4-(4-(2-pyrimidinyl)-l-piperazinyl)butyl) monohydrochloride (U.S. Patent 3,717,634). One of them is follows a mixture of 0.1 mole of the substituted glutaric anhydride, 0.1 mole of l-(4-aminobutyl)-4-(2-pyrimidinyl)piperazine (U.S. Pat. 3,398151), and 300 ml of pyridine was refluxed until imide formation was completed. The degree of reaction was readily followed by taking an aliquot portion of the reaction mixture, removing the solvent, and obtaining the infrared absorption spectrum of the residue. When reaction is complete, the spectrum exhibited typical infrared imide bands at 1701 and 1710 cm-1 whereas if incomplete, the infrared spectrum contains amide and carboxyl absorption bands at 1680, 1760 and 3300 cm 1. 

One of the first VCD studies we undertook in 1988 was work on the tripeptide L-Ala-L-Ala-L-Ala [23], This molecule, in neutral aqueous (D O) solution, exhibits a distinct, near-conservative VCD spectrum in the amide I region, shown in Figure 7. The infrared absorption shows two overlapping peaks in the amide I region, at 1650 and 1675 cm 1. Raman depolarization ratios indicated that the high frequency component is the symmetric stretching combination. 

Figure 9 shows a comparison of the infrared absorption and VCD spectra of (L-Ala), n = 3 - 5. The spectra are normalized for equal absorption intensity at 1595 cm 1, which is the frequency of the carboxylate anion antisymmetric stretching mode. The data show that the amide I intensity increases roughly linearly with the number of peptide linkages in the molecule, and that the VCD intensity increases similarly. However, the positions of the infrared absorption maxima are shifted from about 1654 cm 1 in the trimer to 1648 cm 1 in the pentamer. Similarly, the VCD zero crossing in the trimer occurs at 10 cm 1 higher frequency than in the tetramer and pentamer. We have interpreted these results [48] in terms of different solution conformations of the peptides the trimer seems to be stabilized by zwitterionic interactions, as discussed before, whereas formation of extended helices seems to occur at the level of the tetramer. 

Independent synthesis of the crystalline amide LXVII established its identity and its configurational relationship to L-(+)-mandelic acid. The latter acid was converted to ethyl L-(+)-mandelate (LXVIII), and the ether linkage introduced by reaction with ethyl bromoacetate in the presence of silver carbonate, under conditions such that Walden inversion was impossible. The resulting ethyl D-(+)-2-phenyldiglycolate (LXVI), was subjected to ammonolysis, giving a crystalline product, m. p. 174-174.5°, [a]26D 106.2°. This showed no mixed melting point depression and an identical infrared absorption spectrum with the sample of LXVII obtained from /3-D-xylopyranosylbenzene. The enantiomorphic l-(—)-2-phenyldiglycolamide was also prepared by identical synthetic steps from d-( —)-mandelic acid. 

Fig. 5. (Left) SEIRAS of NaHA and DNA on PAMAM dendrimer SAMs after adsorption for 30 min from aqueous solutions. Dendrimer SAMs were prepared by the amide bond formation of dendrimers with active ester groups of 3-mercapto-propionic acid (MPA) SAMs on CaF2 substrates. Infrared absorption spectra of NaHA, DNA, and PAMAM dendrimer are also included. (Right) Schematic illustration of the interactions between polyelectrolytes and dendrimer SAMs. Reprinted from Ref. [110].

We will show in this section that by applying nonlinear infrared methods, such as IR-pump-IR-probe, dynamical hole burning, and IR photon echoes, one can gather significantly more detailed information on the structure and dynamics of the amide I band than is possible with conventional (linear) absorption spectroscopy. Starting with some knowledge of the underlying contributions to amide I absorption, such as obtained by the aforementioned empirical approaches, nonlinear spectroscopy could provide... 

The synthesis of the allyl ethers in nitrogen heterocyclic systems presents an element of complication in that the allylation could occur on the oxygen atom or the basic nitrogen atom. This is a feature of alkylation of ambident anions.3 However, this applies only when the allylation is effected by reacting the oxo or hydroxy derivative of the compound with an allyl halide in the presence of a base.3 The alternative method is to react the appropriate halo derivative with sodium allyloxide in allyl alcohol. The latter approach provides not only better yields of the allyl ethers but also certainty of the constitution of the ethers obtained. A diagnostic tool in deciding between the 1-allyl derivative and the O-allyl compound that has commonly been employed is the infrared absorption of the amide carbonyl in the case of the former which is clearly absent in the latter. 

Infrared spectroscopy is a valuable tool for the structural analysis of acid derivatives. Ajrid chlorides, anhydrides, esters, amides, and nitriles all show characteristic infrared absorptions that can be used to identify these functional groups in unknowns. 

The model reejuired that two-thirds of the total peptide bonds assume the m-configuration. Yet careful infrared absorption measurements (Badger and Pullin, 1954) showed that collagen contains very few, if any, CTS-amide groupings. Furthermore, Corey and Pauling (1953) themselves pointed out that the frawa-configuration is probably more stable than the... 

The particle beam LC/FT-IR spectrometry interface can also be used for peptide and protein HPLC experiments to provide another degree of structural characterization that is not possible with other detection techniques. Infrared absorption is sensitive to both specific amino acid functionalities and secondary structure. (5, 6) Secondary structure information is contained in the amide I, II, and III absorption bands which arise from delocalized vibrations of the peptide backbone. (7) The amide I band is recognized as the most structurally sensitive of the amide bands. The amide I band in proteins is intrinsically broad as it is composed of multiple underlying absorption bands due to the presence of multiple secondary structure elements. Infrared analysis provides secondary structure details for proteins, while for peptides, residual secondary structure details and amino acid functionalities can be observed. The particle beam (PB) LC/FT-IR spectrometry interface is a low temperature and pressure solvent elimination apparatus which serves to restrict the conformational motions of a protein while in flight. (8,12) The desolvated protein is deposited on an infrared transparent substrate and analyzed with the use of an FT-IR microscope. The PB LC/FT-IR spectrometric technique is an off-line method in that the spectral analysis is conducted after chromatographic analysis. It has been demonstrated that desolvated proteins retain the conformation that they possessed prior to introduction into the PB interface. (8) The ability of the particle beam to determine the conformational state of chromatographically analyzed proteins has recently been demonstrated. (9, 10) As with the ESI interface, the low flow rates required with the use of narrow- or microbore HPLC columns are compatible with the PB interface. 

PMR spectra cannot indicate the presence of amide hydrogen because of rapid exchange of the proton with deuterium oxide solvent. We have found that nitrogen-cobalt bonded complexes with infrared absorptions at 1575 cm. may be formed when N-bromo primary amides react with pentacyanocobaltate(II). Comparison with the spectrum of a complex formed from an N-bromo secondary amide, in which no acidic hydrogen would be present, should help resolve this problem. 

The ether layer is washed successively with 5% hydrochloric acid, 5% sodium carbonate aqueous solution and water, and then dried over sodium sulfate. Upon evaporation of ether, the residue is subjected to fractional distillation in vacuo, thereby to yield 8.9 g. of N-methyl linseed oil fatty acid amide, B.P. 178-190° C./0.03 mm. Hg, I.R. 1,650 cm.-l. (I.R. means wave number of the infrared absorption spectrum.)... 

The infrared absorption spectrum of sulfacetamide sodium has been determined in KBr disc (4). The principal peaks appear at 825, 1090,1145,1264,1552,1600 cm 1. The infrared stretching frequencies of the amino group have been used to calculate the force constant, the band angle and the "S" character of the nitrogen orbitals of the N-H band (23,24). Infrared measurements of sulfonamides have been performed to study the imide-amide tautomerism (25) and to see if there is any change in the electronegativity of the SO2 group (26,27). Sulfacetamide in eye-drops and ointments has been identified by attenuated total reflectance (ATR) infrared spectra (28). 

Decrease of proteinaceous portion, which was associated with decrease of infrared absorptions at 1640 (amide I -t- C=0, etc.) and 1540 cm (amide II). 

Infrared absorption bands related to amide I and II (1640 and 1540 cm ) were lacking in humic acid. 

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